Clinical examination and diagnosis of disease are accomplished by detecting disease-related genes and proteins contained in biological samples using methods such as gene detection, immunological detection and the like. It has been proposed that the electrical current produced by photoexcitation of a photochemically active labeled substance (photoelectrochemical detection methods) should be utilized in methods for the detection of sample substances such as proteins and gene detection methods in clinical examination and diagnosis of disease (for example, refer to U.S. Patent Publication No. 2009/0294305).
U.S. Patent Publication No. 2009/0294305 discloses a method using a test substance such as photochemically active sensitizing dye or the like to detect a sample substance based on the electrical current produced by photoexcitation of the test substance. In the method disclosed in U.S. Patent Publication No. 2009/0294305, a sample substance is labeled with a photochemically active test substance. Then, the labeled sample substance is irradiated with light to photoexcite the sensitizing dye contained in the labeled sample substance. The electrical current produced by the photoexcitation is then measured. The sample substance can be detected with high sensitivity based on the current measurement result. It is desirable to improve detection sensitivity to detect very small amounts of a sample substance.